1. Field of the Invention
The present invention relates to a process for production of carboxylic acid aryl esters. More specifically, the invention relates to a process for production of carboxylic acid aryl esters by a novel reaction not known in the prior art.
2. Description of the Related Art
Aryl esterification of carboxylic acids has conventionally been accomplished by a dehydration reaction between carboxylic acids and phenols, by a method such as (1) using a mineral acid as the catalyst or (2) using a dehydrating agent at an equivalent amount or greater. There is also known a method whereby (3) a carboxylic acid halide and a phenol are reacted to obtain a carboxylic acid aryl ester.
The method of (1) can be applied for production of alkyl esters from alkyl alcohols, but has a drawback in that, with phenols, either no reaction occurs or the reaction yield is very poor.
An example of the method of (2) is described in xe2x80x9cOrganic Compound Synthesesxe2x80x9d (Yuki Kagobutsu Goseiho, by the Society of Synthetic Organic Chemistry, Japan) whereby polyphosphoric acid is used as the dehydrating agent, but since this requires use of the polyphosphoric acid in a large amount, the cost is high and waste water treatment also poses a problem. Japanese Unexamined Patent Publication No. 5-84507 discloses the use of dicyclohexylcarbodiimide as a dehydrating agent, but in this case the dehydrating agent is expensive and a problem is posed in economical terms.
For method (3), a number of documents describe halogenation of a carboxylic acid using a halogen compound such as PCl3, POCl3, PCl5 or SOCl2 followed by reaction with a phenol, but the method involves a complex production process, as a two-stage reaction, and is therefore not a preferred choice.
It is an object of the present invention to overcome the problems associated with the prior art by providing a process for production of carboxylic acid aryl esters which is very simple, easy and inexpensive.
In order to achieve this object, the present invention provides a process for production of carboxylic acid aryl esters which comprises reacting a carboxylic acid having at least one carboxyl group with a di- or tri-aryl phosphite compound represented by the following general formula (1): 
where each R independently represents a hydrogen atom, halogen or alkyl group, m is 2 or 3 and n is 1, 2, or 3, and when there exist a plurality of halogen and/or an alkyl groups as R, they may be the same or different, in the presence of a basic compound and/or water.
The invention further provides a process for production of carboxylic acid aryl esters which comprises reacting a basic salt of a carboxylic acid having at least one carboxyl group with a diaryl phosphite compound represented by the following general formula (2): 
where each R independently represents a hydrogen atom, halogen or alkyl group, n is 1, 2, or 3, and when there exist a plurality of halogen and/or alkyl groups as R, they may be the same or different.
The invention still further provides a process for production of carboxylic acid aryl esters which comprises reacting a carboxylic acid having at least one carboxyl group with a diaryl phosphite compound represented by general formula (2) above.
According to the process of the invention, the reaction may be carried out with the di- or tri-aryl phosphite compound of general formula (1) used in an amount at least equivalent with respect to the carboxyl groups of the carboxylic acid. The reaction is commonly carried out with heating or stirring, and if necessary using a solvent, but the process of the invention is in no way limited to these reaction conditions. The esterification rate will differ slightly depending on the type of carboxylic acid compound used as the starting material, but an esterification rate of 80% or greater, and in most cases 90% or greater, can be easily achieved for a variety of compounds.
Any of various ordinary methods may be employed to recover the desired aryl ester from the reaction system after completion of the reaction. For example, if the reaction product is distillable, it may be distilled off and the product recovered. Alternatively, if the reaction product crystallizes, it may be crystallized out or else dissolved in an appropriate solvent and then cooled to crystallization, and the product recovered.
It has been found that addition of basic compounds or a small amount of water during the process of the invention will promote the reaction. Examples of such basic compounds include alkali metal or alkali earth metal hydroxides, oxides, carbonates and the like.
In the process of the invention, it is believed that when a reaction between the carboxylic acid and a triaryl phosphite compound of general formula (1), where m is 3, is carried out in the presence of a basic compound, a basic salt of the carboxylic acid is produced first while a phenol compound corresponding to a diaryl phosphite compound of general formula (1) where m is 2 is also produced, and then the carboxylic acid basic salt and diaryl phosphite compound in turn react to produce the corresponding carboxylic acid aryl ester and corresponding arylphosphonic acid basic salt. According to the invention, therefore, the target carboxylic acid aryl ester can also be produced by reaction of the carboxylic acid basic salt and diaryl phosphite compound of general formula (1) where m is 2, instead of reaction of the carboxylic acid and triaryl phosphite compound of general formula (1) where m is 3 in the presence of a basic compound. Consequently, the present invention also encompasses a process for production of carboxylic acid aryl esters which comprises reacting the aforementioned carboxylic acid basic salts with diaryl phosphite compounds represented by general formula (2).
On the other hand, it is believed that when the aforementioned carboxylic acid and triaryl phosphite compound of general formula (1), where m is 3, are reacted in the presence of water in the process of the invention, the triaryl phosphite compound first hydrolyzes to produce a diaryl phosphite compound of general formula (1) where m is 2 and the corresponding phenol compound, and then the resulting diaryl phosphite compound and the carboxylic acid react to produce the corresponding carboxylic acid aryl ester and the corresponding arylphosphonic acid. According to the invention, therefore, the target carboxylic acid aryl ester can also be produced by reaction of the carboxylic acid and diaryl phosphite compound of general formula (1) where m is 2, instead of reaction of the carboxylic acid and triaryl phosphite compound of general formula (1) where m is 3 in the presence of water. Consequently, the present invention also encompasses a process for the production of carboxylic acid aryl esters which comprises reacting the aforementioned carboxylic acid with diaryl phosphite compounds represented by general formula (2).